modelling reflections from surrounding buildings

radiance-general
1

Hi,

Just as an aside here. Note that if you do this (ie add an additional gensky call) it will also generate a skyfunc. This could be a problem depending on which order the gensky calls are made.... For example:

   1. gensky with actual sun position
   2. gensky with "reflected" sun position

The second skyfunc for the second gensky is the one that would get applied to the "sky."

Regarding, the original question, I tend to agree with Thomas that the thing to do would be to actually model some simple surfaces to approximate the surrounding conditions.

-Jack

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Lars Grobe wrote:

Hi!

The second block creates the actual sun with the first 3 parameters as
direction vector. This vector needs to be modified by "reflecting" it on
the plan of the reflecting window. You should be able to find the math
for the that on the internet.
    
You can add a line

!gensky [genskyoptions] | xform [xformoption]

To your scene file.

xform will do the translations then. Check the manpage for it, it allows you to perform all necessary rotation, mirror and translation operations.

Just as Thomas, I still do not get want you really want to achieve and why not to use mirror modifiers and real geometry.

Cheers, Lars.

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2

Hi Thomas, Lars and Jack

Thanks for your answers.

The aim is to determine what performance the blinds need for protection.
So I identified a few critical cases, one includes reflection from
surrounding buildings towards the west. These have very reflective
facades, which means that they get some glare on this side during the
mornings. Since it is a rather simple model and because I lack detailed
geometry data of the surroundings, I thought adding a sun in the view
for the as a reflection is a bit quicker than placing a mirror.

Anyway, thanks again.

Greetings from Melbourne

Chris

Kind regards,

Christoph Begert

Associate

sbe

sustainable built environments

Innovative ideas, collaborative design, practical solutions

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________________________________

From: radiance-general-bounces@radiance-online.org
[mailto:radiance-general-bounces@radiance-online.org] On Behalf Of
Thomas Bleicher
Sent: Wednesday, 11 August 2010 6:31 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] modelling reflections from surrounding
buildings

Hello Christoph.

I don't quite understand how you want to create a "reflected" sun
without knowing the position and orientation of the reflecting window.
And if you do know that why don't you just use a "mirror" material for
this window which will create the reflected sun for you?

Anyway, back to creating a second sun:

On Wed, Aug 11, 2010 at 3:36 AM, Christoph Begert - SBE <Christoph.Begert@sbe.com.au> wrote:

  I was thinking of adding another line into my sky file, however
am not totally sure how to exactly do this and was hoping that someone
here could help me with this.

If you look at the output of a gensky command for skies with sun ("+i"
or "+s" option) you will find the definition for the sun; something like
this:

void light solar

0

0

3 6.92e+06 6.92e+06 6.92e+06

solar source sun

0

0

4 0.067845 -0.617210 0.783868 0.5

The definition of "solar" defines the intensity of the sun which you
have to modify according to the reflection of the glazing.

The second block creates the actual sun with the first 3 parameters as
direction vector. This vector needs to be modified by "reflecting" it on
the plan of the reflecting window. You should be able to find the math
for the that on the internet.

The fourth parameter is the size of the sun (in degrees) and can
probably stay unchanged.

Regards,

Thomas

3

Another comment is that adding a sun instead of a mirror assumes an infinitely large reflective facade. Depending on the angle of the sun and maximum height of surrounding buildings there may be times that the sun doesn't actually reflect onto your area of interest. Or there may be situations where your building shadows the reflective façade and reduces the reflection.

Also, the adjacent building would block some portion of the sky contribution to your site - but with the sun definition it adds the reflection without blocking any sky.

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